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w w w . j m r t . c o m . b r

Availableonlineatwww.sciencedirect.com

Original

Article

Eco-friendly

recycled

polypropylene

matrix

composites

incorporated

with

geopolymer

concrete

waste

particles

Flávio

James

Humberto

Tommasini

Vieira

Ramos

a,∗

,

Raphael

Henrique

Morais

Reis

a

,

Iryna

Grafova

b

,

Andriy

Grafov

b

,

Sergio

Neves

Monteiro

a

aMilitaryInstituteofEngineering-IME,Prac¸aGeneralTibúrcio,80,22290-270,Urca,RiodeJaneiro,RJ,Brasil

bUniversityofHelsinki,DepartmentofChemical,KumpulaCampus,A.I.Virtasen,aukio1,P.O.Box55FI-00014,Helsinki,FI,Finland

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Articlehistory: Received1May2019 Accepted14January2020 Availableonlinexxx Keywords: Geopolymerwaste Recycledpolypropylene Eco-friendlycomposites Waterabsorption Tensileproperties

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Civil constructionwasteshave beenincorporated intopolymers forrecycling as novel engineering composites. In the present work eco-friendly composites with recycled polypropylene(rPP)matrixincorporatedwithgeopolymerconcretewasteparticles,wither plain(GCW)orsurface-modifiedwitholeicacid(AGC)wereinvestigated.Thegeopolymer concretewasteparticlesweremixedwithpolymerpowdertoprovideaneffectivedispersion betweenthedifferentmaterials.Compositeswereproducedbyaninitialreactiveextrusion processingfollowedbyinjectionmolding.Thesenovelcompositeswithamountof20,40 and50wt%ofGCWparticles,bothplainas-receivedandsurface-modified,weretechnically evaluated bytensiletests,statisticallyanalyzed byANOVA,aswellasbywater absorp-tionasperASTMstandards.Surfacedispersionofnanoparticleswasrevealedbyatomic forcemicroscopy.Microstructuralanalysiswasperformedbyscanningelectronmicroscopy. TheresultsindicatedthatthesesustainableGCWparticlesincorporatedintorPPmatrix exhibitsuperiorprocessabilityandwaterabsorptionlessthan0.01%.TherPP/AGC compos-itespresentrelativelyhigherelasticmodulus,629MPa,ascomparedtotheneatrPP,with 529MPa.Thesepropertiessuggestpotentialsustainableapplicationsinbuilding construc-tionusingwastematerials.

©2020PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBY-NC-ND license(http://creativecommons.org/licenses/by-nc-nd/4.0/).

1.

Introduction

Theconstructionindustryis,inpastyears,investigating inno-vativematerialstosubstitutetraditionalones,suchaswood, polymers, concrete and metals [1]. In particular, polymer matrixcompositesarereplacingconventionalmaterialsowing

Correspondingauthor.

E-mail:[email protected](F.J.Ramos).

tointrinsic characteristicssuchaslowdensity and plastic-ity. Among these composite those reinforced with natural fibers composea classofsuccessful materialsincreasingly usedinbuildingconstructions[2–5].Itisworthmentioning that,withinthisclass,nanocelluloseisapromising reinforce-mentforpolymercompositeswithspecialproprieties[6–17]. Inadditiontonaturalfibers,wastesfrombuilding construc-tion incorporatedinto polymermatricesconstitute another importantclassofeco-friendlycompositeswithspecific recy-clingpurpose[18,19].

https://doi.org/10.1016/j.jmrt.2020.01.054

2238-7854/©2020PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBY-NC-NDlicense(http://creativecommons.org/ licenses/by-nc-nd/4.0/).

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Pleasecitethisarticleinpressas:RamosFJ,etal.Eco-friendlyrecycledpolypropylenematrixcompositesincorporatedwithgeopolymerconcrete Intermsofthermoplastics,polypropylene(PP)isoneofthe

mostimportantpolymers,producedinlargescaleand com-monlyappliedatseveralsectors,includingtextile,automotive, laboratory equipment, plastic parts and reusable contain-ers.However,itshugepost-consumedvolumehasgenerated worldwide large amounts of urban solid residues. On the otherhand,importantcharacteristicssuchashighchemical stability,stiffness,hardness,toughness,heatresistanceand mechanicalpropertiesstillremaininspentPP,makingitan attractiverecycledwastetobeuseashighperformance com-positematrix[20–23].Indeed,severalworksinvestigatedthe applicationofinorganicfillersinPPmatrixcomposites.Sha etal.[24]investigatedinnovativemethodsoffiller modifica-tionintheproductionofthermoplasticcompositesenabling the increase of the strength, stability of interface bond-ing,highdispersionofparticles andappropriatedrheology. PedrazzoliandPagoretti[25]reportedonthepropertiesofPP compositesreinforcedwithexpandedgraphitenanoplatelets. Zhai et al. [26] investigatedthe recycling asbestos tailings used asfillers inPP composites. Ahmedaet al.[27] inves-tigated the influence of filler loading on the properties of polypropylene/marble sludge compositesand reportedthat the performance of the polymer composites depends on the relationship between the interfaces ofthe matrix and fillers.Chenetal.[28]studiedthe solubilityand diffusivity ofCO2 in polypropylene/micro-calcium carbonate

compos-ites.Theeffectsofthefillersandinterfacebondingcondition betweenthefillersandpolymermatrixwerereportedbythe authors. Etcheverry et al. [29] studied the effect of adhe-sionandmechanicalpropertiesthroughchemicalanchorage ofpolypropylene onto glass fibers, previously treated with methylaluminoxane.Zhuetal.[30]observedtheinfluenceof themontmorilloniteonmechanicalproperties,crystallization andrheologicalbehaviorsofPPcomposites.

Aninnovativematerialdevelopedtoreplaceconventional cementinbuildingconstructionisthegeopolymer,produced fromachemicalreactionofsilica(SiO2)andalumina(Al2O3)

toformaninorganicpolymerbygeopolymerization[31–33].In fact,geopolymershavegainedconsiderableattentionowing totheirintrinsiccharacteristicssuchasfireresistance,high toughnessandlowerCO2emissionsduringproductivecircle,

ascomparedtoPortlandcement[34].Geopolymerscanalso beusedincompositematerials.Ferdousetal.[35]observed theinfluenceofgeopolymerfillersintheproductionofhybrid composites,suchastheredmud,flyashand asbestos tail-ings.As acivil construction cement, ageopolymers might beincorporatedwithadditivessuchassandand pebblesto makeconcrete[36].Duringconstructionandafterdemolition, geopolymerconcretesmaybecomewastesandthuscouldbe recycledbyadditionasasecondphasetoapolymermatrix.A similarsituationmayalsooccurwithaPPproduct,whichafter operationallifebecomesawaste.Inthiscase,theeasytomold thermoplasticPPcouldberecycledascompositematrix.Based ontheaforementionedresults,theobjectiveofthisworkwas toevaluatetheprocessabilityandthetensilebehavioraswell astoperformamicrostructuralanalysisofeco-friendly com-positeswithincorporationofoleic-acidmodifiedgeopolymer concrete(AGC)waste particlesinto therecycled

polypropy-lene(rPP).ForthefirsttimeAGCwasteisincorporatedintoa recycledpolymertodevelopasustainablenovelcomposite.

2.

Materials

and

methods

2.1. Materials

Theplaingeopolymerconcretewaste(GCW),anas-received material, was supplied by Lafarge Concreto Ltda., Brazil. Recycledpolypropylene(rPP),fromproductsmoldedbyblow processingwassuppliedbyCOMBRAREComercialBrasileira deReciclagemLtda.Theoleicacid(99%purity)wassupplied bySigmaAldrich,Brasil.RecycledPPcompositeincorporated withbothplainas-receivedGCWparticlesandoleicacid sur-facemodified(AGC)particleswereinvestigated.

2.2. Materials

Theas-receivedGCWwascrushedinparticlessmallerthan 270meshandtreatedwitholeicacidduring24h,asreported elsewhere[18].ThemodifiedparticlesofAGCweredispersed intomoltenrPPmatrixinascrewextruder.Thetemperature profile,startingfromthefeedingzoneuptothedie,was180, 190and200◦C,whilethescrewrotatingratewasmaintained at6rpm[37].TheproportionsproducedofrPP/AGCcorrespond to80/20,60/40,50/50(m/m%).Pelletsofthemodified compos-iteswereprocessedinaBattenfeldinjectionmachine,Plus35 model.Theblendmixtureswereperformedat200◦C. Accord-ingtoASTMC272[38]andASTMD638[39]standards,water absorptionandtensilepropertieswereevaluated,respectively. Theinfluenceofthemodifierfillerswasobservedduringthe processingoftheAGCspecimens,showinggreaterfluidityand lowtorque,aswellasbettermoldingandprocessabilityfor theAGCcomposites,independentlyoftheamountprocessed. Insteadofwhatwasexpected,ahigherfluiditywasacquired byincreasingtheproportionofmodifiedgeopolymerconcrete into thepolymermatrixoftheAGCcomposites.Thiseffect canbeexplainedbytheplasticizinginfluenceoftheoleicacid fixedonthesurfaceofthehybridfillers,whilewasblended intotherPPmatrix[40].

Atomicforcemicroscopy(AFM)wasperformedto evalu-ate theagglomeratedandsurfaceconditionofthepolymer composites.ObservationwascarriedonaXE7equipment, pro-ducedbyParkSystem.

Water absorptionevaluationasperASTM C272[38]was performedtoevaluatethepercentageofwaterabsorptionin therPPaswellasinbothrPP/GCWandrPP/AGCcomposites, consideringtheresultsofsevenspecimensforeach.

TensiletestsasperASTMD638[39],werecarriedouton auniversalmodel1185Instronmachine.Theelastic modu-lus (between0.05%and0.25%strains)atacrossheadspeed of5.105mm/min,andtensilestrengthatthesamecrosshead speed,oftherPP/AGCcompositeswerecalculated.Analysisof variance(ANOVA)wasperformedforstatisticalvalidationof thepropertiesobtainedfromtentensile-testedspecimensof eachtypeofcomposites,includingtherPP(0%AGC).

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Fig.1–(a)Elasticmodulus;(b)tensilestrength,and(c)maximumdeformationvariationwithrecycledpolypropylene(rPP) compositesincorporatedwitholeicacidmodifiedgeopolymerconcretewaste(AGW).

Table1–Waterabsorption(wt%)ofinjectionmolded recycledpolypropylene(rPP)compositesincorporated withplaingeopolymerconcretewaste(GCW)andoleic acidmodifiedgeopolymerconcretewaste(AGC).

FractionofAGC Incorporation(wt%) rPP/GCW rPP/AGC 0 0.01 ≤0.01 20 ≤0.01 ≤0.01 40 ≤0.01 ≤0.01 50 ≤0.01 ≤0.01

3.

Results

and

discussion

Table 1 presents the results of water absorption tests for purerPP,0%geopolymerconcretewaste,aswellasforboth rPP/GCWandrPP/AGCcomposites.Accordingtotheseresults, all investigated materials absorbed practically no amount (≤0.01%) ofwater, what corroborates previous results [18]. They also indicate no significant effect of capillary water absorptionbygeopolymerconcreteincorporatedintothePP

matrix,whichrevealsconsistentlyembeddedplainGCWand modifiedAGCintorPP.

ThetensilepropertiesoftherPP/AGCcompositespecimens and therPPmatrix (0%AGC) arepresentedinTable2.The observedresultsshowthe influenceofthe highamountof modifiedAGC fillersintothematrix.Tensileresultsforthe rPP/GCW composites were less significant for this present investigation and,therefore, are notpresentedherein. The goodinteractionbetweenmodifiedAGCandrPPenablesthe increaseoftheelasticmodulusofthecompositesbythe incor-poration of modified geopolymer concrete waste particles. Furthermore,theresultsshowthattherPPmatrixdecreasethe maximumdeformationfrom42.7%toabout24%,stabilizing thislevelatthe40–50%AGCproportions.Theincreaseofthe elasticmodulusisanindicativeofagoodadhesionbetween matrix/fillers.Consequently,thecompositesacquiredsuitable stiffness capacityfor civil construction applications. These resultscorroborates thosealready obtainedforPP incorpo-ratedindustrialwastes[26,27,29].

Fig. 1 shows the graphs corresponding to the results presentedinTable2.Asforthevariationoftheelastic

mod-Table2–Tensilepropertiesofrecycledpolypropylene(rPP)compositesincorporatedwitholeicacidmodifiedgeopolymer concretewaste(AGC).

FractionofAGCincorporation(wt%) TensileStrength(MPa) ElasticModulus(MPa) MaximumDeformation(%)

0 33.5±1.6 529.1±33.9 42.7±2.6

20 26.8±1.4 534.1±25.3 34.6±3.6

40 22.0±0.8 618.2±31.2 24.6±0.8

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Pleasecitethisarticleinpressas:RamosFJ,etal.Eco-friendlyrecycledpolypropylenematrixcompositesincorporatedwithgeopolymerconcrete

Fig.2–SEMfractographyofrecycledpolypropylene(rPP)compositesincorporatedwitholeicacidmodifiedgeopolymer concretewaste(AGC)inconditionsofpreviousextrusion(a),(c)(e);andfinalinjectionmolded(b),(d),(f).

Fig.3–Atomicforcemicroscopyofrecycledpolypropylene(rPP)compositesincorporatedwith:(a)20wt%and(b)50wt%of oleicacidmodifiedgeopolymerconcretewaste(AGC).

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Table3–Analysisofvariance(ANOVA)parametersfor tensilepropertiesofrecycledpolypropylene(rPP) compositesincorporatedwitholeicacidmodified geopolymerconcretewaste(AGC).

AnovaParameters F Fc P

TensileStrength 161.32 3.01 4.88×10−16

ElasticModulus 12.04 3.01 5.25×10−5 MaximumDeformation 109.18 3.01 4.00×10−14

ulus, Fig. 1(a) reveals a significant increase in the elastic modulusabove20%incorporationofoleicacidsurface treated-geopolymerconcretewaste.Thiscorrespondstoaneffective reinforcementinthestiffnessofrPP/AGCcomposites.By con-trast, the tensile strength, Fig. 1(b), and maximum (total) deformation,Fig.1(c),sufferadecreasewithAGC incorpora-tion.Thereasonfortheseadverseresultsinthestrengthand deformationmightbeattributedtogeneration ofcracks as furtherdiscussedregardingthemicrostructuralevolution.

ThedatapresentedinTable2andshowninFig.1were validatedbyANOVA.Table3presentsthevaluesoftheANOVA parametersF,Fcritical(Fc) andP.Inthistable,considering that5%(0.05)isthelevelofsignificance,valuesofF>Fcare associatedwith95%ofconfidenceinthedifferencebetween them.Moreover,ifP<0.05,asignificantdifferencemightbe consideredbetweenvalues.

AsshowninTable3,basedontheANOVA,the incorpora-tionofmodifiedAGCintorPPcausesastatisticallysignificant increaseintheelasticmodulus.Inotherwords,the hypothe-sisthatthevaluesarethesamecanberejectedwith95%of confidence.

Fig.2showsSEMfractographsof20,40and50%AGC incor-porated into rPP composites, each one in both processing conditionsofinitiallyextruded,Fig.2(a),(c)and(e),andfinally moldedbyinjection,Fig.2(b),(d)and(f).Theinitiallyextruded conditionrevealsafractureassociatedwithmoreporesthen thefinallyinjected.Thisclearlyindicatesthatthesecondstage ofinjectionprocessinghassignificantlydecreasedthe poros-ity, mainlyfor50% AGC compositeingoing from extruded condition,Fig.2(e),tomold-injected,Fig.2(f).Itconfirmsan effectiveencapsulatingofthegeopolymerconcretewaste par-ticles by the recycled polypropylene matrix. This porosity elimination afterinjectioncorroborates thepractically null waterabsorptionresultsinTable1.Ontheother hand,the injectedspecimensdisplayevidenceofcracksaspointedfor the40and50% AGCcompositesinFig.2(d)and(f), respec-tively.Thiscrackingobservationcouldexplainthedecreasein strengthandtotaldeformationinTable2andFig.1.

Fig.3showsAFMresultsfortwoinvestigatedextreme con-ditionsofrPPcomposites,with20and50%AGC.Thisfigure evidencesthechangeinroughness,fromarelativelysmother surfaceforthe20%AGCcompositeinFig.3(a)toarougher surfaceforthe50%AGCinFig.3(b).Actually,thecauseof sur-faceroughnessforthe50%AGCcompositemightbeassigned totheagglomerationofoleicacidmodifiedgeopolymer con-cretewastenanoparticles,aspointedbyarrowsinFig.3(b). TheresultsinFig.3disclosethesignificantinfluencethatAGC particlespromoteinthecompositesurfacetopography.As dis-cussed,theresultsinFig.2forthe50%AGCcompositeindicate aneffectiveencapsulatingcondition,whichshouldbe

inter-pretedasgood adhesionbetweenparticles andrPPmatrix. Thisisapparently confirmedbythewell matrix-embedded AGC particles pointed in Fig.3(b), whichcertainly favorsa stiffnessreinforcementpresentedinTable2anddepictedin

Fig.1(a).

4.

Summary

and

conclusions

• Eco-friendlycompositeswithrecycledpolypropylene(rPP) matrixincorporatedwith20,40and50wt%ofgeopolymers concretewasteparticles,bothplainas-received(GCW)and oleicacidsurface-treated(AGC)wereforthefirsttime pro-cessedandcharacterized.

• Aninitialextrusionfollowedbyinjectionmoldingresultin rPP/AGCcompositesdisplayinggreaterfluidityin associa-tionwithlowextrusiontorqueaswellasimprovedmolding ifcomparedwithrPP/GCWcomposites.

• Practicallynowaterabsorption(≤0.01%)wasfoundforboth typesofrPP/GCWand rPP/AGC composites,includingfor purerPP.

• The incorporation of AGC particles above 20wt% signif-icantly increases the elastic modulus of the rPP matrix. However, this incorporation reducesthe tensile strength andtotalstrain.

• SEMfratographsrevealedaneffectivereductionof poros-ityduringprocessingfromextrusiontoinjectionmolding, whichjustifythenullwaterabsorption.However,cracking aftermoldingwouldberesponsiblefordecreaseinstrength andstrain.

• AFMdiscloses evidence ofrougher surface due to parti-clesagglomerationincompositewithhighamountofAGC, whichmightfavortheobtainedstiffnessreinforcement.

Conflicts

of

interest

Theauthorsdeclarenoconflictsofinterest.

Acknowledgements

The authors thank the Conselho Nacional de Desenvolvi-mento CientíficoeTecnológico(CNPq)andCoordenac¸ão de Aperfeic¸oamentodePessoaldeNívelSuperior(CAPES)for sup-portingthiswork.

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